DE3221357A1 - Process for the production of moulds and cores for casting purposes - Google Patents

Abstract

A layer of binder is applied to the surfaces of a pattern or core box, mould material is introduced and compressed, and the layer of binder is hardened to a shell, while the mould material enclosed by, and supporting, the shell remains free of binder. The process is distinguished by being versatile and adaptable to different binder systems and mould material systems, and leads to a reduced quantity of binder, better disintegration or easier release of the mould part after casting, to better surface properties of the castings, and better gas permeability in spite of compression being more easily performed. The process is particularly suited to the production of cores for light metal castings.

Description

PROCESS FOR MANUFACTURING MOLDS AND CORES FOR CASTING PURPOSES

The invention relates to a method for producing molds and Cores for casting purposes, hereinafter referred to as mold parts.

A large part of the mold parts consists of granular, refractory inorganic raw materials, mostly sand, whose granules are hardened by high molecular weight or are bound by swellable substances, the binding agent. With the known In this process, a molding material is mixed from the base material and the binding agent and by introducing or applying in or

Shaped into molded parts on core boxes, models or model plates and thermally and / or chemically to block forms and solid cores or shell forms and Hollow cores hardened or compacted.

In the production of solid mold parts according to the known method The disadvantage is that the entire molding material is mixed with a smock and solidifies. This leads to increased costs due to high binder consumption, to more expensive Depaning or reprocessing of the used sand, sometimes not enough Gas permeability of the mold wall and unsatisfactory surface quality of the castings, to not always sufficient disintegration of the molded part after casting and thus to difficulties in demolding and great effort in cleaning, in particular with cores for cast parts with less heat supply such as in light metal castings and with thin-walled parts. Furthermore, there are nuisances from the $ h, ermic decomposition larger proportions of binder to possibly.

Clean and odorous gases and the costs of eliminating them.

The use of the known shell molding processes, such as e.g.

This mask molding process according to Croning, in principle, allows the above Avoiding or limiting disadvantages is necessary but curing of the shell molding through heat transfer from the heated effective surface of the model or core box and thus special, expensive heat-resistant models and core boxes, which are not profitable for small numbers of castings. The one for the croning procedure Generally used molding material made of quartz sand coated with phenol-formaldehyde novolak e.g. only hardens in a temperature range of 280 to 310 OC in a sufficiently short time the end. The shell thicknesses that can be achieved in this case are mostly, especially in the case of cores unevenly and often lead to melt breakthroughs during casting.

This problem must then either be due to increased expenditure on molding material for continuous core wall reinforcement up to the approach to the volikern with its disadvantages mentioned above or by an additional, complex filling be solved using binder-free filler material.

Therefore, for technical or economic reasons, it does not have to cured molding material are often left in the molded part, which is caused by the heating during casting to complete hardening and correspondingly insufficient core disintegration with Difficulty removing cores and cleaning leads. Often there is even a subsequent Annealing treatment necessary for complete core removal.

The recently known and partially used vacuum forming process dispenses with a binding agent and uses air pressure with the aid of a film for the cohesion of the molding material. However, this method has the disadvantage the effort for generating and maintaining the necessary negative pressure and the restriction to shallow depths of form; in addition, no cores could be produced from this up to now.

The invention is based on the object with the help of a novel Method and a device developed for this purpose, the disadvantages of the above Procedures to avoid and optimal conditions for rational use of To ensure molded parts in casting production.

The object is achieved according to the invention in that the binder for itself on the effective surface of the model, the model plate or the core box or is applied to these simulated surfaces before they are applied with molding material will.

This is advantageously achieved in that on the active surfaces, ie the surfaces of the model, the model plate or the core box that form the contour of the molded part determine one or more layers of binder of variable thickness with a suitable viscosity by spraying, brushing on, dipping, pouring over, Fall pouring, dusting, melting, condensing, sublimating and others application methods known per se are applied.

To facilitate separation, to increase stability and to To improve the surface quality, it is also advantageous to use one or more layers of binder on a thin shell or skin that previously formed the effective surfaces of the model, the model plate or the core box was simulated to apply, so that a composite layer is achieved with combined properties that are not achieved by the individual layers can be achieved.

The applied material can consist of molding material binders known per se of organic or inorganic nature in pure form or in a combination different binders exist. It can hardeners, accelerators, stabilizers, Foaming agents, solvents, viscosity-determining additives, oxidizing agents, Release agents, sizes and other additives adapted to the specific application that promote the molding process, improve the molding surface and the Facilitate demoulding. It can be liquid, solid, powdery or pulpy, as a solution, Suspension, emulsion or foam.

According to the requirements of the production process, either immediately after application of the binder layer or, after intermediate storage, at a later point in time the molding material by pouring in, shooting in, blowing in, Shaking or other filling methods of mold production in or applied and compacted, with molding material grains more or less deep in the Binder layer penetrate.

The molding material can be pure granular, refractory inorganic material or a mixture of such substances. For economic reasons it mostly comes here Quartz sand with or without the addition of clay minerals for use. Next to it are also all other molding materials known in foundry technology are suitable, such as zirconium and chromite sands, metal powder, salts and the like.

The molding material can be mixed with water, hardening agents, accelerators, oxidizing agents, Depolymerization catalysts and others adapted to the specific application Be provided with molding additives that improve the bond with the binder and promote decay after decanting.

In order to have sufficient green stability, especially in the case of large molded parts To achieve this, an additional binder in the molding material can also be advantageous, its concentration, however, is well below the amounts added in conventional molding material systems can lie.

For the compaction that is necessary even with binder-free molding material basically all known methods can be used. Particularly suitable is a simple process that is performed by means of a flexible membrane and simultaneous pressure Vibration compresses the pourable molding material with comparatively little energy.

After the binder layers according to the chosen system chemically and / or thermally hardened or solidified by physical processes is and has formed a dimensionally stable shell, is removed from the mold.

In order to achieve the required ease of removal from the mold, the Surfaces of the model, model plate or core box made of non-stick material, in particular anti-adhesive plastics, executed or in a known manner with Treated release agents.

The use of one corresponding to the active areas is also advantageous deformed or deformable of the model, the model plate or the core box thin carrier material as a separating film, e.g. plastic films, also water - or alcohol-soluble, impregnated papers, nonwovens, etc.

The advantages that can be achieved with the invention are essentially derived on the characteristic feature of the method according to the invention that the molded parts are completely enclosed by the binder cover, while with the conventional Process, as far as they work with binding agent, every single grain of binding agent is wrapped.

This leads to a considerable reduction in the amount of binder and thus at lower cost, reduced environmental impact due to reduced decomposition products as well as to reduce the landfill volume or the amount of used sand to be regenerated.

The thin-walled binding agent scale falls off even when the heat supply is low and thus facilitates the core removal of the cast parts considerably, which is a significant simplification and reducing the cleaning work.

In the conventional process, the quality of the casting surface is through the grain structure of the molding material is shaped, unless it is subsequently applied Sizing the roughness is reduced. Acts in the method according to the invention the binder itself layers like a size.

The gas permeability of the molded parts required during casting is also increased by the new process, because the bulk material is free of binders offers sufficient gas-permeable pore space. Also the binder layer interspersed with grains In practical tests it has proven to be well gas-permeable - especially in the foamed one Condition - proven.

-The absence of binder shells around each individual bulk material grain facilitates the compression of the molding material and reduces the compression energy considerable.

A particular advantage of the method according to the invention is that that the most diverse binder and molding material systems in a simple manner Can find what the method is particularly adaptable to the different use Problems with the casting of metals, plastics and inorganic-non-metallic Materials. So omitted E.g. the difficulties with not sufficiently long processing time of a conventional molding material mixture, because now the hardener is brought directly to the shaping surfaces at the same time as the binding agent can be. Furthermore, the use of binder systems that are cold or harden quickly with a slight increase in temperature, without the use of poisonous or dangerous hardeners easily possible, which makes the use cheaper and easier to process A large selection of model materials is possible.

Finally, there are particular advantages in the production of Molded parts whose destruction after casting is not due to thermal decay, but is carried out by dissolving the binder with the aid of a solvent.

For example, a core can be made from a dried salt layer or a layer of gypsum slip as a binder coating and consist of binder-free sand, which is removed from the casting after pouring with water. Unlike compact ones Salt or gypsum cores here are the entire core surface from the inside to the solvent Easily accessible so that the thin layer of binder disintegrates quickly.

Claims (12)

PATENT CLAIM: 1. Process for the production of molded parts for the casting of metals, plastics and inorganic-non-metallic materials, d u r c h e k e n n n z e i c h n e t that the binding agent for itself on the Active surfaces of the model, the model plate or the core box is applied, before these are applied with molding material. 2. Process for the production of molded parts for the casting of metal, Plastics and inorganic-non-metallic materials, characterized that the binder for itself on the surfaces of a thin shell, which is the active surfaces of the model, the model plate or the core box are applied before they are applied with molding material. 3. The method according to claim 1 and 2, characterized in that the binder organic or inorganic in nature used in pure form or as a combination will. 4. The method according to claim 1 and 2, characterized in that the Binder one or more additives from one or more of the groups a) hardeners b) curing accelerators c) stabilizers and inhibitors d) foaming agents or Propellants e) solvents, emulsifiers and suspending agents f) viscosity-determining agents Additives g) oxidizing agents h) release agents i) sizing agents. 5. The method according to claim 1 and ~ 2, d a d u r c h g e k e n n z e i c h n e - t that the binding agent by spraying on, brushing on, dipping, pouring over, Lintel pouring, dusting, melting, condensing or sublimating applied will. 6. The method according to claim 1 3Wd 2 and 5, characterized in that that the binder is applied as a foam or with foam formation. 7. The method according to claim 2 and 5, characterized in that the Binder on a corresponding to the active surfaces of the model, the model plate or of the core box deformed or deformable thin carrier material is applied. 8. The method according to claim 1 and 2, characterized in that the Molding material made from binder-free base material or from a mixture of binders free base materials of groups a) oxides b) metal powder c) salts. 9. The method according to claim 1 and 2, characterized in that the Molding material contains a binder according to claims 3 and 4, the concentration of which is essential is lower than with conventional molding material systems. 10. The method according to claim 1 and 2, characterized in that the Molding material one or more additives from one or more of the groups a) curing agents b) hardening accelerator c) oxidizing agent d) depolymerization catalysts or contains a water additive. 11. A method for compressing pourable molding material according to claim 8, 9 and 10, characterized in that by pressure over a flexible membrane and simultaneous vibration is compressed. 12. Process for demolding or core removal from castings with molded parts according to claims 1 and 2, characterized in that after removal of the free-flowing molding material, the binder coating is removed by solvents.